efficient market theory

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Efficient Market Theory

Dr. Rana Singh

Associate Professor

www.ranasingh.org

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Efficient Capital Markets

In an efficient capital market, security prices adjust rapidly to the arrival of new information, therefore the current prices of securities reflect all information about the security

Whether markets are efficient has been extensively researched and remains controversial

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Why Should Capital Markets Be Efficient?

The premises of an efficient market• A large number of profit-maximizing

participants analyze and value securities• New information regarding securities

comes to the market in a random fashion• Profit-maximizing investors adjust security

prices rapidly to reflect the effect of new information

Conclusion: the current price of a security should reflect its risk

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Alternative Efficient Market Hypotheses

Weak-form efficient market hypothesis Semistrong-form EMH Strong-form EMH

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Weak-Form EMH

Current prices reflect all security-market information, including the historical sequence of prices, rates of return, trading volume data, and other market-generated information

This implies that past rates of return and other market data should have no relationship with future rates of return

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Semistrong-Form EMH

Current security prices reflect all public information, including market and non-market information

This implies that decisions made on new information after it is public should not lead to above-average risk-adjusted profits from those transactions

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Strong-Form EMH

Stock prices fully reflect all information from public and private sources

This implies that no group of investors should be able to consistently derive above-average risk-adjusted rates of return

This assumes perfect markets in which all information is cost-free and available to everyone at the same time

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Tests and Results of Weak-Form EMH

Statistical tests of independence between rates of return• Autocorrelation tests have mixed results• Runs tests indicate randomness in prices

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Comparison of trading rules to a buy-and-hold policy is difficult because trading rules can be complex and there are too many to test them all• Filter rules yield above-average profits with

small filters, but only before taking into account transactions costs

• Trading rule results have been mixed, and most have not been able to beat a buy-and-hold policy

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Testing constraints• Use only publicly available data• Include all transactions costs• Adjust the results for risk

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Results generally support the weak-form EMH, but results are not unanimous

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Tests and Results ofSemistrong-Form EMH

Studies to predict future rates of return using public information beyond market information• Time series analysis• Cross-section distribution

Event studies examine how fast stock prices adjust to significant economic events

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Tests and Results of Semistrong-Form EMH

Test results should adjusted a security’s rate of return for the rates of return of the overall market during the period considered

Arit = Rit - Rmt where:

Arit = abnormal rate of return on security i during period t

Rit = rate of return on security i during period t

Rmt =rate of return on a market index during period t

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Tests and Results ofSemistrong-Form EMH

Arit = Rit - E(Rit)

where: E(Rit) = the expected rate of return for stock I during

period t based on the market rate of return and the stock’s normal relationship with the market (its beta)

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Time series tests for abnormal rates of return• short-horizon returns have limited results• long-horizon returns analysis has been

successful based on– dividend yield (D/P)

– default spread

– term structure spread

• Quarterly earnings reports may yield abnormal returns due to

– unanticipated earnings change

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Tests of standardized unexpected earnings (SUE) normalize the difference in actual and expected earnings by the standard error of estimate from the regression used to derive the expected earnings figure SUE =

Reported EPSt - Predicted EPSt

Standard Error of Estimate for the Estimating Regression Equation

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Large SUEs result in abnormal stock price changes, with over 50% after the announcement

Unexpected earnings can explain up to 80% of stock drift over a time period

These are evidence against the EMH Additional tests include calendar studies

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The January AnomalyStocks with negative returns during the prior

year had higher returns right after the first of the year - studies indicate an excess return on AMEX but not on NYSE

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Other calendar effects• All the market’s cumulative advance occurs

during the first half of trading months• Monday/weekend returns were significantly

negative

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Predicting cross-sectional returnsAll securities should have equal risk-adjusted

returns Studies examine alternative measures of

size or quality as a tool to rank stocks in terms of risk-adjusted returns• These tests include a joint hypothesis and

are dependent both on market efficiency and the asset pricing model used

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Price-earnings ratios and returns• Examine historical P/E ratios and returns• Stocks are divided into five P/E classes• Low P/E stocks had higher returns and had

lower risk• Publicly available P/E ratios could be used

for abnormal returns• This is inconsistent with semistrong

efficiency

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•Tests and Results of Semistrong-Form EMH

The size effect (total market value)• All stocks on NYSE and AMEX were ranked by

market value and divided into ten equally weighted portfolios

• The risk-adjusted returns for extended periods indicate that the small firms consistently experienced significantly larger risk-adjusted returns than large firms

• Could this have caused the P/E results previously studied?

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•Tests and Results of Semistrong-Form EMH

The P/E studies and size studies are dual tests of the EMH and the CAPM

Abnormal returns could occur because either • markets are inefficient or • market model is not properly specified and

provides incorrect estimates of risk and expected returns

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Adjustments for riskiness of small firms did not explain the large differences in rate of return

The impact of transactions costs of investing in small firms depends on frequency of trading• Daily trading reverses small firm gains

The small-firm effect is not stable from year to year

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Neglected Firms• Firms divided by number of analysts following

a stock• Neglected firm effect caused by lack of

information, crosses size classes• Contradictory results from another study

Trading volumeStudied relationship between returns, market

value, and trading activity

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Firm size has emerged as a major predictor of future returns

This is an anomaly in the efficient markets literature

Attempts to explain the size anomaly in terms of superior risk measurements, transactions costs, analysts attention, trading activity, and differential information have not succeeded

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Book value-market value ratio• As a predictor of stock returns• Significant positive relationship between the

current values for this ratio and future stock returns are evidence against EMH

Size and BV/MV dominate other ratios such as E/P ratio or leverage

This combination only works during expansive monetary policy

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Event studies• Stock split studies show that splits do not result

in abnormal gains after the split announcement, but before

• Initial public offerings seems to be underpriced by about 15%, but that varies over time, and the price is adjusted within one day after the offering

• Being listed on an exchange may offer some short term profit opportunities

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Event studies (continued)• Unexpected world events and economic

news are quickly adjusted to and do not provide opportunities

• Announcements of accounting changes are quickly adjusted for and do not seem to provide opportunities

• Corporate events such as mergers and offerings are adjusted to within a few days

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Summary on the Semistrong-Form EMH

Evidence is mixed

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Evidence is mixed Strong support from numerous event

studies with the exception of exchange listing studies

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Studies on predicting rates of return for a cross-section of stocks indicates markets are not semistrong efficient

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Studies on predicting rates of return for a cross-section of stocks indicates markets are not semistrong efficientDividend yields

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Studies on predicting rates of return for a cross-section of stocks indicates markets are not semistrong efficientDividend yields, risk premiums

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Studies on predicting rates of return for a cross-section of stocks indicates markets are not semistrong efficientDividend yields, risk premiums, calendar

patterns

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patterns, and earnings surprises

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patterns, and earnings surprises This also included cross-sectional

predictors such as size, the BV/MV ratio (when there is expansive monetary policy), E/P ratios, and neglected firms.

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Tests and Results of Strong-Form EMH

Strong-form EMH contends that stock prices fully reflect all information, both public and private

This implies that no group of investors has access to private information that will allow them to consistently earn above-average profits

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Testing Groups of Investors

Corporate insiders

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Corporate insiders Stock exchange specialists

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Corporate insiders Stock exchange specialists Security analysts

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Corporate insiders Stock exchange specialists Security analysts Professional money managers

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Corporate Insider Trading

Insiders include major corporate officers, directors, and owners of 10% or more of any equity class of securities

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Insiders must report to the SEC each month on their transactions as insiders

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Insiders must report to the SEC each month on their transactions as insiders

These insider trades are made public about six weeks later and allow for study

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Corporate insiders generally experience above-average profits especially on purchase transaction

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Corporate insiders generally experience above-average profits especially on purchase transaction

This implies that many insiders had private information from which they derived above-average returns on their company stock

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Studies showed that public investors who traded with the insiders based on announced transactions would have enjoyed excess risk-adjusted returns, but the markets now seem to have eliminated this inefficiency (soon after it was discovered)

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Other studies indicate that you can increase returns from using insider trading information by combining it with key financial ratios and considering what group of insiders is doing the buying and selling

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Stock Exchange Specialists

Specialists have monopolistic access to information about unfilled limit orders

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You would expect specialists to derive above-average returns from this

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You would expect specialists to derive above-average returns from this

The data generally supports this

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Security Analysts

Tests have considered whether it is possible to identify a set of analysts who have the ability to select undervalued stocks

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Security Analysts

Tests have considered whether it is possible to identify a set of analysts who have the ability to select undervalued stocks

This looks at whether, after a stock selection by an analyst is made known, a significant abnormal return is available to those who follow their recommendation

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The Value Line enigma

Value Line (VL) publishes financial information on about 1,700 stocks

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The report includes a timing rank from 1 down to 5

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Firms ranked 1 substantially outperform the market

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The Value Line Enigma



Firms ranked 1 substantially outperform the market

Firms ranked 5 substantially underperform the market

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Changes in rankings are quickly price adjusted into the market

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Changes in rankings are quickly price adjusted into the market

Some content that the Value Line effect is merely the unexpected earnings anomaly due to changes in rankings from unexpected earnings

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Security Analysts

There is evidence in favor of existence of superior analysts who apparently posses private information

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Efficient Markets and Technical Analysis

Technical analysts develop systems to detect movement to a new equilibrium (breakout) and trade based on that

Contradicts EMH rapid price adjustments

If the capital market is weak-form efficient, a trading system that depends on past trading data can have no value

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Efficiency in European Equity Markets

Hawawini study indicates behavior of European stock prices is similar to U.S. common stocks

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Future topicsChapter 9

Analysis of Financial Statements Financial Ratios Evaluating Performance

efficient market theory

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